1. Technical Field
This invention relates to improvements to a torque converter for use with an automatic transmission, and more particularly to an improved torque converter that increases the gas mileage and horsepower of a vehicle.
2. Description of Related Art
FIG. 1 is a side view of a vehicle 400 having an engine 200 and a transmission 300 connected by a torque converter 100. In a vehicle 400 with an automatic transmission, the torque converter 100 provides the link between the engine 200 and the transmission 300.
FIG. 2 is an exploded view of a prior art original equipment (“OE”) torque converter, or torque converter that is originally a part of the vehicle when the vehicle is sold. The prior art torque converter has a drive member 112 attached to an engine crankshaft or flywheel and an impeller/pump 102 that is generally adjacent the transmission. The impeller/pump 102 is attached to the cover 104, typically by a welded seam. Residing within the cover 104 is a one-half inch friction lining (transverse direction) disposed upon a ledge 138 of metal that is welded to the inside of the cover 104. The OE friction lining and ledge height (axial direction) can be 0.115 inches. The friction-lined ledge 138 frictionally engages with the piston 116 within the cover 104 and thus rotates upon engagement with the cover 104.
The torque converter is typically filled with a viscous fluid such as automatic transmission fluid. Once the engine is started, the drive member 112 and cover 104 rotate at engine speed. Because the impeller 102 is attached to the cover 104, the impeller 102 also rotates at engine speed, or at impeller revolutions per minute (RPM). Fluid enters through the input shaft/drive member 114 into the cover 104 and then towards the impeller 102. The impeller 102 has a series of longitudinal fins, vanes, or blades, which drives the fluid around the outside diameter of the impeller 102 into the turbine 106. The impeller 102 thus functions like a centrifugal pump. This pumping of fluid transfers power from the impeller 102 towards the turbine 106 and causes the turbine 106 to rotate. The turbine 106 is attached to a drive member 114 via a spline to the input shaft 114 of the transmission. When the turbine 106 rotates, the vehicle moves.
Although the impeller 102 rotates at engine speed (“Impeller RPM”), the turbine 106 must overcome a load to begin rotation. For example, the Impeller RPM must produce enough energy to permit the turbine 106 to overcome the resistance to move the vehicle from a resting position. The number and shape of the impeller and turbine blades has an impact on the efficiency of the torque converter. Because the blades help to channel the fluid to provide a driving force, substantial torsional forces are imparted on the blades, increasing the likelihood of distortion or failure over time. Failure and distortion of the traditionally tack welded impeller and/or turbine blades is undesirable because it affects the fluid driving force flow paths which can lower efficiency of power transfer from the impeller 102 to the turbine 106. In addition, failure can cause metal pieces of the blades to be deposited into the transmission fluid. This can result in further damage to various moving and non-moving parts in the torque converter and transmission alike. Consequently, there is a need for impeller and turbine blades that can better withstand torsional forces.
The torque converter typically operates in two modes—stall mode and lock-up mode. Stall mode is when the Impeller RPM is greater than the Turbine RPM. The torque converter is in stall mode during vehicle acceleration. In the stall mode, a torque converter can create a torque multiplier effect. A torque multiplier effect occurs when more torque is output to the drive wheels than the engine is actually producing. This can result in more horsepower and greater fuel efficiency. A typical torque converter will have a torque multiplication ratio of about 2.5:1. Lock-up mode is when the Impeller RPM is substantially equal to the Turbine RPM. The ratio of the Turbine RPM to the Impeller RPM defines the amount of hydrodynamic slippage. Mechanical slippage can and does occur in areas where the moving parts frictionally engage.
As the Impeller RPM increases during acceleration, the turbine 106 moves axially toward the cover 104 and pressure is applied against the piston 116 and the friction lined ledge 138 inside of the cover 104. The fluid entering through the input shaft 114 near the thrust washer 151 causes fluid to apply back pressure (force directed away from cover 104) to the piston 116 and prevents lock-up. An electric solenoid controls the flow of fluid through the input shaft 114 and thereby adjusts the centrifugal force on the piston 116. For example, when the solenoid stops the flow of fluid through the input shaft to the cover 104, back pressure on the piston 116 is eliminated and the torque converter goes into lockup, meaning that the turbine 106, piston 116, and the friction lined ledge 138 inside the cover 104 frictionally engage one another and lock. One problem with this design is that the torsional forces can overcome the frictional forces resulting in mechanical slippage. Mechanical slippage can occur when the cover 104 RPM is greater than the piston 116 RPM. As slippage increases, fuel efficiency and horsepower decreases. It is therefore desirable to decrease the amount of slippage and/or the amount of time that the torque converter is in the stall mode.
As previously discussed, the stator 110 changes the fluid flow between the impeller 102 and the turbine 106 and is responsible for the torque multiplier effect. During vehicle acceleration, the torque converter is in the stall mode. The stator 110 redirects and further accelerates fluid as it returns from the turbine 106 through the stator 110 fins in an outward radial direction to increase the amount of engine torque transferred between the impeller 102 and the turbine 106 and acts as a torque transfer multiplier. As a result, Turbine RPM is able to more efficiently approach the Impeller RPM, thereby reducing slippage. Thus, the torque converter 100, principally due to the stator 110, helps to reduce slippage and thereby increases fuel efficiency and horsepower. Changes to the stator 110 that can enhance torque converter efficiency are desirable. Consequently, a need exists to improve the stator to further improve fuel efficiency and horsepower.
FIG. 3 is an exploded view of a prior art after market torque converter 100. Residing within the cover 104 is a first ring 120 and a second ring 122. The first ring 120 has a first side facing the cover 104 and a second side facing the impeller/pump 102. Similarly, the second ring 122 has a first side facing the cover 104 and a second side facing the impeller/pump 102. The first ring 120 has a friction lining 126 on the first side. The second ring 122 has a friction lining 128 on the first side and a friction lining 130 on the second side. The second ring 122 has a set of tabs splined to the lugs within the cover 104 and thus rotates upon engagement with the cover 104. The cover 104 turns at engine speed. The first ring 120 has a set of tabs that are splined to the lugs on the piston 116 and thus rotates with the piston 116. The first ring 120 and second ring 122 make up the clutch pack 118. The clutch pack 118 and the piston 116 make up the lock up clutch 108. The piston 116 is splined to the turbine 106 and thus rotates with the turbine 106.
As the Impeller RPM increases during acceleration, the turbine 106 moves axially toward the cover 104 and pressure is applied against the piston 116, rings 120 122 and the inside of the cover 104. At a certain lock-up pressure, the piston 116, rings 120 122 and cover 104 frictionally engage one another and lock. Upon engagement, the inner, raised portion of the piston 116 (not shown) mates with a thrust washer 151 attached to the center of the cover 104. The purpose the torque converter design is to transfer torsional forces from the rings 120 122 to the cover 104 and the piston 116. Upon lock-up, the clutch pack 118 and thrust washer 151 is subjected to extreme torsional forces. These torsional forces can lead to premature failure of the thrust washer 151, rendering the torque converter inoperable. In addition, failure of the thrust bearing can cause metal filings to be deposited within the transmission fluid, which can further cause damage to the transmission and the torque converter. Consequently, there is a need for an improved torque converter that is less prone to failure.